1. Field of the Invention
The present invention relates to a toner for electrophotography and a developer composition including the toner. More specifically, the present invention relates to a toner for electrophotography having not only excellent transparency demanded for a toner, particularly for a color toner but also excellent fixing ability and blocking resistance, and a developer composition including such a toner.
2. Discussion of the Related Art
Recently, even in color copy machines, owing to high-speed recording rate and miniaturization of the copy machines, there is an urgent demand for a development for a binder resin for toners which can be fixed at an even lower temperature.
However, in the high-speed recording rate and the miniaturization, there arises such a problem that when continuous copying is carried out for a large number of copies, heat of a heat roller is taken away by an image-supporting member and heat cannot be supplemented in time, so that the temperature of the heat roller is lowered, thereby causing fixing failures.
On the other hand, there has been known that the molecular weight of a binder resin for toners is lowered in order to improve the low-temperature fixing ability ("Fine Chemical," 22, 7 (1993)). However, simply lowering the molecular weight would also cause a decrease in the glass transition temperature. As a result, there arises such a problem that the resulting toner would have poor performance in the blocking resistance, as evaluated by toner agglomeration under environmental conditions upon storage.
In addition, in full-color electrophotography, since development is carried out for a plurality of times, and several kinds of toner layers having different hues are laminated on the same image-transferring material, transparency of the resin and smoothness of a fixing surface upon fixing are demanded. Therefore, more strict conditions are demanded for full-color electrophotography in addition to such properties as a wide fixing temperature range and excellent offset resistance which are demanded for mono-color copy machines.
On the other hand, as the copying machines are more generalized, they are highly likely to be used under severe environmental conditions, for instance, under high-temperature, high-humidity conditions or under low-temperature, low-humidity conditions. Therefore, a toner capable of obtaining formed images as clear as those obtained under normal conditions even under such severe environmental conditions is becoming increasingly crucial.
As described above, it has been extremely difficult to have appropriate hardness in the toner and at the same time have basic toner properties, such as blocking resistance, triboelectric charge stability, and low-temperature fixing ability, and the full-color toner properties such as transparency and smoothness of the fixing surface.
An object of the present invention is to provide a toner for electrophotography which has excellent blocking resistance, triboelectric charge stability, and low-temperature fixing ability, thereby making it less likely to undergo changes in the above properties even under severe environmental conditions such as low-temperature, low-humidity conditions or high-temperature, high-humidity conditions, and has high transparency and is able to form a smooth fixing surface; and a developer composition including the above toner.
These and other objects of the present invention will be apparent from the following description.